How to Find the Numbers of IPs on Subnets

Determine how many IP addresses can exist on your subnet.

Within the same Local Area Network (LAN), each computer receives a unique Internet Protocol (IP) address. The number of IP addresses allowed by the configuration of a LAN (referred to as the size of the subnet) determines, therefore, how many computers can be simultaneously connected to the LAN. You can find out the number of IP addresses allowed by your subnet.

Instructions

1. Determine the subnet mask (a special IP address needed for LAN routing) for your LAN: click "Start," then type "run" into the search box, then press "Enter" and click on "Run." Enter "cmd" into the newly-opened Run window and press Enter. Click on the newly-opened Command window and type "ipconfig /all."

   Press "Enter." The mask is listed immediately after the "Subnet Mask" heading in the "ipconfig" output.

2. Translate the subnet mask into binary, one number at a time. For example, 255.255.252.0 gets translated into 11111111.11111111.11111100.00000000.

3. Count the number of ones in the binary version of the mask; call it M. For the example, M equals 22.

4. Evaluate the following formula:

   numberIPs = (2^(32-M))-2.

   NumberIPs is the number of IP addresses allowed in your subnet. For the example, addressSpace equals (2^(32-22))-2 = 1022.

References

• Internet Engineering Task Force: Address Allocation for Private Internets